Which PMI ACP 11 reference book should if buy for giving the PMI ACP exam? Is it available in PMI site as the PMBOK? or Where can I buy it from? Also do I have to read this book before attempting the exam?

You are not required to buy anything. Course covers everything. Each and every topic of these books is not relevant from the PMI-ACP content outline. We have to filter and course has done that part for you.

You can refer a success story where it is mentioned: "My preparation Journey start from Izenbridge and end on same"